Save output of os.system to text file

Question

I\'m not great on all the technical terms so I\'ll do my best to explain my problem.

I\'ve written a small script to open android SDK and check for attached devices

Answer 1

Try the following:

import os 
import subprocess 
import time 

print ('Current Directory: {}'.format(os.getcwd()) ) 
print ('Opening Android SDK...') 
os.chdir('C:\\android-sdk\\platform-tools') 
print ('Current Directory: {}'.format(os.getcwd()) )
t = str(time.ctime()) 
try:
    process_output = subprocess.check_output(["adb", "devices", "-l"])
except: #Add here the type of exception you want to raise and logic
    print("Please check your ADB installation and syntax.")
s = ('{} Checking for connected devices: {}'.format(t,process_output) ) 
with open('logfile.txt', 'w') as f:
    f.write(s) 

Answer 2

os.system executes the command in a subshell and returns the command's exit code. It does not provide any mean to capture the outputs of the command ("outputs" => what the command prints to it's stdout/stderr streams).

To capture the command's outputs you'll have to use some of the subprocess module's feature, the most obvious here being subprocess.check_output

# ...
import subprocess
# ...
# NB : you may want to catch subprocess.CalledProcessError here
out = subprocess.check_output(['adb',  'devices', '-l'])
msg = "{t}\nChecking for connected devices:\n{out}".format(t=t, out=out)
with open('logfile.txt', 'w') as f:
    f.write(msg)

Answer 3

With Python 3.5+ you can (and probably should) use subprocess.run() which conveniently replaces the legacy subprocess.check_output() with a more versatile API.

import subprocess

with open('logfile.txt', 'w') as f:
    subprocess.run(['adb', 'devices', '-l'], stdout=f,
        universal_newlines=True)  # this obscurely makes everything Unicode

Directly connecting the stdout of the subprocess to an open file handle is possible via the old check_output() API too, mind you.

Answer 4

Thanks everyone for your help. The answer was:

import os
import time
import subprocess

print 'Current Directory:', os.getcwd()
print 'Opening Android SDK...'
os.chdir('C:\\android-sdk\\platform-tools')
print 'Current Directory:', os.getcwd()
print 'Checking for connected devices:'
t = time.ctime()
# save log of time and connected devices
with open('logfile.txt', 'w') as f:
    s = ('{}\n{}'.format(t, subprocess.check_output(["adb", "devices", "-l"])))
    f.write(s)
print(s)